As is well known, a mechanical pencil has a problem that a drawn line width may change because a writing lead locally abrades as the writing proceeds.
The present applicant has previously proposed a mechanical pencil with a rotational drive mechanism in which the writing lead is gradually rotated in one direction using writing pressure applied to the writing lead. This is disclosed in Patent Documents 1, 2, and the like.
According to this mechanical pencil, when the mechanical pencil is used to perform writing with a body cylinder inclined to the writing side (page) at around 40 to 80 degrees, for example, each time a stroke is drawn, the writing lead is slightly rotationally driven in one direction, so that a tip portion of the writing lead is always kept sharp in the shape of a cone. Therefore, the mechanical pencil allows writing with almost the same line width.
There are other proposals for mechanical pencils with a rotational drive mechanism for writing lead. For example, a mechanical pencil disclosed in Patent Document 3 has a rotatable cam with upper and lower cam faces continued in a circle that is integrated in a slider protruded to the front of a body cylinder. The mechanical pencil is configured such that first and second fixed cams are alternately meshed with the upper and lower cam faces of the rotatable cam within a base member positioned on the outside of the slider.
Further, Patent Document 4 discloses a configuration of a mechanical pencil in which a first cam face is formed in a circle in a base member and a second cam face is formed in a circle in a stopper member attached to the rear end of the base member. A cam protrusion is protruded in a direction orthogonal to an axial direction from a side surface of a sleeve rotating together with a chuck holding a writing lead. In the mechanical pencil, a lead rotational mechanism is configured such that a cam protrusion is provided on a side surface of a sleeve rotating with a chuck grasping a writing lead, and the cam protrusion is orthogonal to the axial member and travels between the first cam face and the second cam face.